Adhesive free fiber reinforced laminate

ABSTRACT

By very rapid and precise electronic controlled heat application, with conditions held between specified critical limits, Applicants have succeeded in producing reinforced laminates without the use of adhesives, and yet retaining the capacity of the reinforcements to move controllably in response to stresses so as to present maximal tear resistance.

United States Patent Yaeger et al.

[4 1 Feb.12,1974

ADHESIVE FREE FIBER REINFORCED LAMINATE Inventors: Luther L. Yaeger;Wei-Gwo Chen,

both of Houston, Tex.

Assignee: Griffolyn Company, Incorporated,

Houston, Tex.

Filed: Feb. 23, 1972 Appl. No.: 228,783

Related U.S. Application Data Continuation of Ser. No. 871,916, Oct. 28,I969, abandoned.

U.S. C1 161/58, 156/77, 156/179, 161/59,161/143,161/151,161/161,161/402Int. Cl B321) 5/12 Field of Search.... 156/179, 77; 161/57, 58, 59,161/140,142-144,151, 161, 402

[56] References Cited UNITED STATES PATENTS 2,719,100 9/1955 Banigan161/402 X 3,471,353 10/1969 Rasmussen... 161/402 X 2,861,022 11/1958Lundsager [61/402 X Primary Examiner-William A. Powell Attorney, Agent,or Firm-W. F. Hyer [57] ABSTRACT By very rapid and precise electroniccontrolled heat application, with conditions held between specifiedcritical limits, Applicants have succeeded in producing reinforcedlaminates without the use of adhesives, and yet retaining the capacityof the reinforcements to move controllably in response to stresses so asto present maximal tear resistance.

11 Claims, 7 Drawing Figures ADHESIVE FREE FIBER REINFORCED LAMINATEThis application is a continuation of Ser. No. 871,916, filed Oct. 28,1969 (now abandoned).

PRIOR ART This invention relates to reinforced plastic laminates and hasfor its object an inexpensive method for producing such laminates athigh speed.

Heretofore laminates have been made by applying adhesive to plasticfilm, feeding in the reinforcing fiber between said films and thenlaminating them together, or by heat sealing films together with fibersor scrim between them, by means of heated roller, or by high frequencyheating, so as to melt the films together, or it has been furthercontemplated to feed metallic pigment between the films and heat this bymeans of induction heating, and further to apply the fibers to one film,and immediately extrude the second film thereunto so that the secondfilm would envelop the reinforcing fibers and bond them to the base.

These methods have the disadvantages respectively that the applicationof adhesive calls for a multiple step operation and for adhesivecompounding and handling, usually also entailing solvent recovery. Theprocesses based on heat sealing the films together so as to envelop thereinforcement are disadvantageous because application of the heat willcertainly break down any reinforcing or strengthening effect oforientation in the film layers and maybe even in the fibers. The methodof applying metal pigment to the center and heat sealing thisselectively by induction heating of metallic pigment has thedisadvantage that the said metallic pigments add to cost, and do notcontribute to the strength of this fabric; furthermore, that beingparticulate, they will tend to cause local overheating at the pointscontacted by the pigments whether these be large or even very small, andfurther that induction heating is an expensive form of heat.

OBJECTIVES An object of the present invention is to effect lamination byhighly superficial heat applications, so that even when films one milthick and thinner are employed, only less than 15 percent of the filmsthickness will be actually brought to an adhesive state and at least 70percent of the films thickness will not be weakened.

Another object is a superior fibrous laminate made at low cost.

Another object is a machine for producing reinforced laminate at lowercost and equal or better quality, than has previously been attained.

A further object is improvements in the art of making flexible, foldablelaminates.

Further objects will become apparent as the following detaileddescription proceeds.

DRAWINGS In discussing this invention, we make reference to thedrawings, of which FIG. 1 is a schematic cross-sectional diagram of theapparatus employed, showing also the process. FIGS. 2, 3 and 4 show theproducts prepared by the use of this process. FIG. 5 is a detailedperspective view and FIG. 6 is a detail of the apparatus in section.FIG. 7 is a side sectional view of the laminate. The

drawings are given only to illustrate the invention and are not intendedas limitations.

DESCRIPTION OF THE INVENTION In accordance with our invention, we feednonwoven thermoplastic filaments into the bite between laminatingrollers, while closely regulating speed and temperature so that only theinner surface layers of the films are softened by the heat, while themajor part of the film retains its previous orientation and strength.While passing thru the laminating zone, the softened inner surfaces ofthe films flow together and fuse, to form an intermediate non-orientedlayer, in which the fibers are held, so as to provide a laminateconsisting essentially of 3 layers: Two outer highly oriented films, andbetween these a single layer of a lower degree of orientation, if any,in which are held the reinforcing fibers, and which has been formed by afusion of material originating from both of the first mentioned films.

Referring to FIG. I, 1 and 2 are rollers supplying the thermoplasticoriented films 3 and 4 to the laminating means which in this caseconsists of the laminating rollers 5 and 6. These rollers may be heatedor cooled electrically or by circulating fluids; these details have notbeen shown because they are not essential to the invention. Because ofthe necessity for extremely rapid and sensitive heat modulation, weprefer to use electrical means for heating. The heating means 9 arepreferably electrically energized heaters, through they might also begas controlled radiators or jets of heated gas such as air or nitrogenor steam.

The reinforcing fibers are supplied from a creel 14 to an angularizer13, which arranges the fibers in preselected patterns of non-wovenessentially parallel groups of fibers 12. These are then fed into thelaminating means between the films 3 and 4.

While the films and fibers travel into the laminating means at a speedof at least 20 ft/min and preferably over 200 ft/min, and may be broughtto speeds even an order of magnitude higher, their inner surfaces arevery rapidly and exactly heated by heating means 9 so as to bring abouta softening of the innermost layers to the point that orientation issubstantially nil, and the layers flowable so that on contact they willhold the fibers and fuse into a single essentially amorphous layer. Thismay, if desired, be re-oriented by subsequent drawing, if drawing of theoriginally supplied fibers is incomplete, but it does preserve anidentity distinct from that of the outer film layers.

The necessary delicate control of the heat source may be supplied asfollows: A radiation type photofiux meter is pointed at the films justas they enter the bite. This instrument (such as Thermodot, built byIrcon, Inc., Skokie, Ill.) can sense the temperature by radiationwithout touching the actual surface it is measuring, and has thesensitivity and electronic speed (from millisecond to microsecond range,the latter with an indium antimonide sensor in the instrument) whichmakes it possible for it to govern the heating means with such precisionand speed, that the outermost surface of the films can be fused in aconstant manner, say to as little as 0.01 percent thereof or as much as40 percent thereof in films having a thickness from r mil to 12 mil, orin laminates having an aggregate thickness between 1 mil and 10 mil; orso that the depth of heat penetration sufficient to cause plastic flowinstantaneously can be regulated with about IO percent accuracy at anylevel of penetration between 20 percent of the total thickness and 0.01mil.

To effect this close control in a fast moving web, the output from thephoton flux temperature sensor 10 is processed by a computer 1 l, whichin turn sends anticipating instructions to the heating means which maybe single or multiple, and advantageously also to the speed regulatingmeans for the driving mechanisms.

From the laminating means and 6 the laminate produced may move to acrosslinker 15, which may be an electron beam generator or a substanceemitting ionizing radiation, such as Cobalt 60, or an ultra-violetradiator, or even a chamber in which the laminate passes through agaseous crosslinking medium such as for example formaldehyde for anaminoor hydroxy resin film, or hydrazine for a carboxyl resin likeacrylic acid, or a diamine for a polyvinyl chloride film, and the like.

This crosslinking treatment is not usual, but can be applied when highdimensional stability is required.

The laminate 7 thus produced is taken up on roll 8.

FIG. 2 shows a top view of a longitudinal film laminate with a singlefiber layer 16 thus produced, FIG. 3 of a diamond pattern with non-wovenfibers 17 and 18 where the difference from the prior art of US. Pat. No.2,851,389 is that the slidability of fibers which is essential tomaximal tear strength has been attained for the first time at highproduction speeds without the use of any adhesive.

FIG. 4 shows a laminate.

FIG. 5 is a detail view showing how the angulated fibers enter thelaminating means and FIG. 6 shows in detail how the lamination occurs,with the fusion of the heated layers on the insides of the films.

FIG. 7 shows how the fibers may be held in the fused layer withoutnecessarily being wholly surrounded by it. This occurs particularly whenthe heating conditions are selected to produce minimal fused layers, yetsufficient to attach the fibers to both films. In this case, theaggregate fused disoriented layer 23 is thinner than the diameter of thefibers, so that the laminate bulges EXAMPLE Using the procedure andapparatus described above in conjunction with FIG. 1, laminates wereprepared of l A to 10 mil films of the plastics stated below. The filmwas supplied at a speed of ft/min. Infrared lamps were used as the heatsource together with polished parabolic reflectors placed at a distanceof I 6 to 3 inches from the laminating rollers. Initial runs were madewith manual control, for higher speed operation the lamp heat output wasgoverned by modulating the signal output from a Thermodot photon fluxradiometer.

Immediately following the lamination, we cooled the film by air jets tobelow 200F immediately after leaving the pressure rollers. Aftertraveling a couple feet, the surface temperature was below 100F.

The take-off roller was provided with a clutch for constant pull tensiontake-off, to be controlled by the operator who tightened the tensionwhen any tendency to wrinkling appeared, but otherwise kept it as looseas possible in order to avoid stretching of the film. This became touchywith films of l /2 and 2 mils.

The line power used was 220 V, and was varied by power stat, graduallyincreasing it from 50 Volts to about 180 to 200 Volts. The rotationalspeed of the laminating rollers was controlled by a hand cranktransmission, starting at 0 and gradually increasing the speed to the 20ft/min which was operational speed for the pilot machine used in thisinitial run. For full speed operation, it is envisaged to go to 400 to500 ft/min with increase in heat radiation applied, so that theradiometer surface temperature just as the film enters the bite betweenthe laminating rollers will be low enough to permit the instant heatweld described, generally above the softening temperature of the plasticused in the film.

The total effective heating width was 2 inches. It is not believed thatthis will require major modification for speed increases, inasmuch asthe thickness of the softened surface layer is less important to bondingthan is the temperature, and the temperature can be brought to thedesired level by increasing the intensity of the heating to match theincreased speed.

At the beginning of the run, the laminating rollers were preheated by aninternal heating coil (steam would have done as well) to 150F. Thisrequired about 2 minutes within this time the operational conditionsshould be reached by the other parameters:

Voltage of power supply from 50 to 200 V Temperatures at the laminatingrollers from to 400F within a couple feet and following the laminatingroll to F Linear speed from 0 to 20 ft/min In several runs of an hoursduration, the above conditions could be maintained easily and no furtheradjustment was needed once the parameters had reached desiredequilibria. Runs were made with polyethylene, polypropylene (both highdensity and low density of these), polyvinyl chloride (plasticized,extruded), polyethyleneglycol terephthalate, fusible polyurethane film,and nylon film. All of these were found suitable after minor operationalvariations well within the skill of the operator.

As reinforcing material we used 420 Denier nylon fiber, both preshrunkand regular, polyethylene gylcol terephthalate, polypropylene slitribbons, glass fibers, and polyvinyl chloride coated glass fibers.

While all of these gave useful results, we preferred for adhesion anduniformity the laminates made using polyvinyl chloride with any of thefibers, and high density polyethylene, or any of the polyolefins whenloaded with 3 to 8 percent carbon black, preferably with acrylate orpolyolefin fibers.

Weathering tests with the film laminates thus produced showed nodeterioration compared with conventional adhesive laminates.

ALTERNATIVES To determine the time required to effect the desiredlimited heating of a portion of the film, without affecting the strengthof the bulk of the film, we calculated the time required for raising theoriginal temperature of 70F to 160F by means of an air blast at 500, 600and 700F, in a 2 mil polyethylene film, to a depth of 10 percent of thethickness.

Using the conductivity heat flow equation H KA(AT)(Time)/d where KConductivity heat transfer coefficient s seconds of time H Heat requiredC, Specific Heat AT Temp. difference between air blast temp. and

0.2 mil depth temp. original temp. of 70F 11 depth in film A Area DDensity AC (5/9)AF and assuming the following approximations:

pec ific hea t C 1 cal./gm./C Density-D=1 gmJcc? Heat conductivitycal./C/sq.cm./cm./second Time [(C,,)D/4K]d [(l) (1)/4(.a-10*)]K (PH-210*in seconds for d in cms. we arrived at the following theoretical values:

Time required for heating Air blast temperature depth of 2 mil film to160 500F 0.35 milliseconds 600F 0.31 milliseconds 700F 0.29 millisecondsBased on this, air heating under the conditions postulated would permitproduction at the rate of at least 590 ft/second assuming a 2 inchheating zone in contact with air at 700F.

Thus, the rate of surface heating, whether by air or steam orelectricity, will not be a limiting factor in the speed of production,but at high speeds the ease of control will be important. For thisreason, electrical radiation heating is preferred.

To arrest the infrared radiation in the surface layer and cause heatingin this layer preferentially, we may add to the film an infraredabsorbent substance, such as for example 0.05 to 5 percent of acompatible iron compound, such as ferric naphthenate of ferric octoate,or the ferric salt of a vinyl carbonic acid, such as acrylic acid.

The present invention is not directed to the materials used to producethe laminates; any thermoplastic or heat fusible film of good mechanicalproperties can be used. For the guidance of those desiring to use theinvention, the following materials are listed as suitable, but any otherfusible and mechanically satisfactory polymer film can be used:polyolefins, such as polypropylene and polyethylene, polyvinylpolyvinly' halides such as polyvinyl chloride and fluoride; celluloseacetate, fluorocarbon films such as polytetrafluoro ethylene, polyesterfilms such as diethylene glycol terephthalate, polyphenoxide films,polyimid films such as polybenzimidazol, and the like. It is generallypreferred to use fibers spun from the same or similar polymers,

keeping in view that it is easiest to preserve the fiber strengthundamaged if fibers are used which do not become disoriented at thetemperatures of fusion of the films with which they are used. We preferto use fibers which do not become disoriented below the disorientationtemperatures of the films; however if the fibers are more than twice asthick as the disorientation zone of the films under the operatingconditions used, it is possible to use almost any pair of plastic andfiber that would occur to those skilled in the art.

Having thus disclosed our invention, we claim:

1. A flexible, foldable, adhesive-free plastic laminate which comprisestwo layers of molecularly oriented plastic, a layer of molecularlydisoriented plastic separating these oriented layers, said disorientedlayer having a thickness between 0.0012 mils and 4.8 mils whichthickness is also not more than 40 percent nor less than 0.01 percent ofthe thickness of the laminate, and substantially molecularly orientedorganic polymer fibers imbedded in said disoriented layer.

2. The plastic laminate of claim 1, in which the said oriented layershave an aggregate thickness between 1 mil and 10 mi], and thedisoriented layer common to them has a thickness between 0.01 mil and 40percent of the total thickness of the laminate.

3. The plastic laminate of claim 1, in which the said organic polymerfibers have a thickness exceeding that of the disoriented layer, and thesaid disoriented layer is bonded to two sides of the said fiber, leavingthe intermediate zones thereof substantially unbounded.

4. The plastic laminate of claim 1, in which the first mentioned plasticlayers are crosslinked in addition to being oriented.

5. The laminate of claim 1, in which the said organic polymer fibers areheld firmly, yet with a strength less than the tear strength of saidlaminate, so that on application of tear stresses the said fibers willslide and bunch forming bundles which prevent the propagation of tear.

6. The laminate of claim 5, in which the said disoriented layer has beencrosslinked so as to make the said laminate substantially dimensionallystable.

7. The laminate of claim 5, in which the said substantially orientedorganic fibers form a diamond pattern.

8. The laminate of claim 5, in which the adhesion of the said fiberswithin the laminate is weakened by air bubbles along the sides of saidfibers, thereby rendering these slidable within the said laminate inresponse to directional stresses.

9. The laminate of claim 5, in which said laminate contains an addedinfrared absorbing substance.

10. The laminate of claim 5, in which the laminate contains between 0.05percent and 5 percent of its weight of a compatible ferric compound.

11. The laminate of claim 5, in which the plastic is a

2. The plastic laminate of claim 1, in which the said oriented layershave an aggregate thickness between 1 mil and 10 mil, and thedisoriented layer common to them has a thickness between 0.01 mil and 40percent of the total thickness of the laminate.
 3. The plastic laminateof claim 1, in which the said organic polymer fibers have a thicknessexceeding that of the disoriented layer, and the said disoriented layeris bonded to two sides of the said fiber, leaving the intermediate zonesthereof substantially unbounded.
 4. The plastic laminate of claim 1, inwhich the first mentioned plastic layers are crosslinked in addition tobeing oriented.
 5. The laminate of claim 1, in which the said organicpolymer fibers are held firmly, yet with a strength less than the tearstrength of said laminate, so that on application of tear stresses thesaid fibers will slide and bunch forming bundles which prevent thepropagation of tear.
 6. The laminate of claim 5, in which the saiddisoriented layer has been crosslinked so as to make the said laminatesubstantially dimensionally stable.
 7. The laminate of claim 5, in whichthe said substantially oriented organic fibers form a diamond pattern.8. The laminate of claim 5, in which the adhesion of the said fiberswithin the laminate is weakened by air bubbles along the sides of saidfibers, thereby rendering these slidable within the said laminate inresponse to directional stresses.
 9. The laminate of claim 5, in whichsaid laminate contains an added infrared absorbing substance.
 10. Thelaminate of cLaim 5, in which the laminate contains between 0.05 percentand 5 percent of its weight of a compatible ferric compound.
 11. Thelaminate of claim 5, in which the plastic is a polyolefin.